1. Field of Invention
The invention relates to a speed-difference-dependent hydraulic coupling, consisting of a rotating gear housing which is stationary, a housing which forms a reservoir for operating fluid, a hydrostatic displacement machine in the gear housing, a drive shaft, and a friction coupling to connect the drive shaft with the gear housing and a piston to have an impact on the friction coupling, by which pressure is created in a pressure chamber when there is a differential speed between the gear housing and the drive shaft, which influences an impact on the friction coupling, and by which the hydrostatic displacement machine is provided with a first and second opening for the supply and discharge of operating medium and a third and fourth opening for connection with the pressure chamber.
2. Description of the Prior Art
These type of couplings are being applied in various configurations in the motive power line of motor vehicles to directly transfer a torque or to block a connected differential power transmission to drive the wheels of an axle or for distribution of the starting torque between two axles. The hydrostatic displacement machine consists, for example, of an internal rotor and an external rotor. However, hydrostatic displacement machines of other types of construction can also be used. In any case when there is a differential speed, two parts (e.g. drive housing and output shaft) perform a relative motion and create an impacting pressure on the pistons of the friction coupling.
This type of coupling is renowned, for example, from U.S. Pat. No. 5,536,215. In this case, a valve of a bimetallic laminar will be provided between the pressure chamber and a space with lesser pressure, i.e. the coupling area. This valve shall compensate viscosity changes of the operating fluids, which depend on the temperature. Other regulating devices will not be provided.
As disclosed in U.S. Pat. No. 4,727,966 (hereinafter xe2x80x9c""966xe2x80x9d), another such coupling in a slightly different arrangement is renowned. In this type of coupling, discharge openings with restrictors will be provided between the third and fourth openings and the pressure chamber. These discharge openings enable different set pressures for the two possible directions of the differential speed, i.e. a difference between the driving and delayed operations, or forwards and reverse speeds.
Furthermore, as shown in FIG. 7 of the ""966 reference, regulating devices are already provided, i.e. more discharge valves, the set pressure of which can be regulated. The adjusting signal for this will be determined by a control device of different operating sizes. The control devices are installed in the rotating part. Thus, the adjusting signals, in this case hydraulic, must be fed to them by a rotating entry. The pressure on the suction side of the displacement machine will not be influenced. All of this and in addition the impact of the centrifugal force on the regulating devices makes a delicately sensitive, exact and quick regulation impossible.
In German Patent Document Number DE 198 54 867 A, another similar coupling is renowned in another arrangement, by which the pressure chamber itself, rather than the displacement machine, is connected by a rotating entry with a control valve equipped with a rigid housing for pressure modulation on the pressure side. In this way only an imperfect control is possible. Therefore, in order to tow the motor vehicle, the displacement machine must be made completely pressureless, which necessitates a valve on the suction side. Furthermore, the valve arrangement requires the coupling unit to be constructed in such a way that it has a number of other disadvantages.
The aim of this invention is to further develop a coupling which is of a kind that ensures a delicately sensitive, exact and quick regulation and adaptation of the characteristic with at least expense as possible.
The above aim of the invention is achieved in that the streams of the first and second openings, respectively, are connected to the reservoir by a first and second rotating entry and a first and second valve with rigid housings, and that the first and second valves are formed as regulating throttle valves, so that independent of the direction of the differential speed, there will be a control action on the supply as well as on the discharge side of the displacement machine.
Therefore, control valves will be provided at the shortest way to and from the displacement machine on the pressure and suction sides, which have direct impact on the coupling with very little delay in all driving conditions possible. Since these are controllable throttle valves, i.e. arranged in the main stream, it is possible to control over the entire regulating range in a delicately sensitive and exact manner.
There are also the following advantages of the arranged control valves in rigid housings; simple connection with the control device, no disturbing influences of the centrifugal force, no restrictions of the size and good access. Furthermore, due to these advantages, the supply and discharge of the operating medium is possible on the side of the displacement machine, so that the rotating insertions could be provided relatively simple at small diameters. The additional costs for the rotary transmission is made competitive due to the omission of the necessary non-return valves without both control valves in the same line.
In one embodiment of this invention, the first and the second valve forms a common control valve. Apart from the reduction in costs in this connection, improvement of the reliability without any loss in the function capability in the driving operation is also achieved. During this, the first and second valves could be controlled by proportional valves or by a stepping motor.
In a further embodiment of this invention, a double-acting non-return valve will be provided between the third and fourth openings and the pressure chamber. Due to the fact that one side is always open at this valve, the pressure chamber above this valve and the regulating valve can be made pressureless very quickly, which is of an advantage especially when braking (ABS, ESP). Furthermore, the valve can be installed in the wall between the displacement machine and the pressure chamber which especially saves space. Acceptable transition from one type of operation to the other is ensured by the fact that there is only one valve with one circuit element (preferably with a ball).
An advantage of this invention is that the common control valve is formed by a movable adjusting piston in a sleeve. The sleeve is connected to the streams of the reservoir on both sides and has a first and second lateral control opening. The pressure side of the displacement machine is connected with the first control opening and the suction side of the displacement machine is connected with the second control opening.
During operation, the adjusting pistons close the first and the second control openings in its two end positions and more or less close the two control openings in the two intermediate positions in countercurrent. Due to this, the rate of opening and closing of both valves is achieved with less construction costs. Space efficiency and accessibility are further improved if the sleeves of the control valve have a plane arrangement transversal to the revolution axis of the coupling in the area of the rotating insertions.
Another advantage of this invention is that the double-acting non-return valve consists of a tangential bore in a plane arrangement transversal to the revolution axis of the coupling and a locking device therein between the displacement machine and the pressure chamber. Both ends of the tangential bore are connected to the third and fourth openings of the displacement machine and its center point to the pressure chamber. In this way the valve is not influenced by the centrifugal force in case of minimal space requirement.